Synthesis of 1,3-Difunctionalized Cyclopentenes and 1,3,5-Trifunctionalized Cyclohexanes by Silicon-Induced Domino Reactions

A novel domino process based on a 1,4-C⇄O shift of a silyl group (4 ⇄ 3) and a Michael-induced ring-closure reaction (3 ⇄ 2) is investigated. Specifically, attack of carbanions 5 on vinyloxiranes 6 usually occurs on the oxirane unit to give the desired silyl shift. When starting from vinyloxiranes 6a and 6b, however, the reaction stops at this stage to give silyl ethers 7. Sulfur (6c) or silicon activation (6d−f) of the C=C unit is required to yield cyclopentenes 1a−d. Analogously, carbanion 5a and allyloxiranes 15 give cyclization products 19−22, particularly if the ring-closure step is supported by silicon substitution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)